diff --git a/addons/userrights/userrightsprofile.class.inc.php b/addons/userrights/userrightsprofile.class.inc.php
index 11331350e..ca0f596c1 100644
--- a/addons/userrights/userrightsprofile.class.inc.php
+++ b/addons/userrights/userrightsprofile.class.inc.php
@@ -533,7 +533,7 @@ class URP_ClassProjection extends UserRightsBaseClass
 		MetaModel::Init_AddAttribute(new AttributeExternalKey("dimensionid", array("targetclass"=>"URP_Dimensions", "jointype"=> "", "allowed_values"=>null, "sql"=>"dimensionid", "is_null_allowed"=>false, "on_target_delete"=>DEL_MANUAL, "depends_on"=>array())));
 		MetaModel::Init_AddAttribute(new AttributeExternalField("dimension", array("allowed_values"=>null, "extkey_attcode"=> 'dimensionid', "target_attcode"=>"name")));
 
-		MetaModel::Init_AddAttribute(new AttributeClass("class", array("class_category"=>"", "more_values"=>"", "sql"=>"class", "default_value"=>"", "is_null_allowed"=>false, "depends_on"=>array())));
+		MetaModel::Init_AddAttribute(new AttributeClass("class", array("class_category"=>"", "more_values"=>"", "sql"=>"class", "default_value"=>null, "is_null_allowed"=>false, "depends_on"=>array())));
 
 		MetaModel::Init_AddAttribute(new AttributeString("value", array("allowed_values"=>null, "sql"=>"value", "default_value"=>"", "is_null_allowed"=>false, "depends_on"=>array())));
 		MetaModel::Init_AddAttribute(new AttributeString("attribute", array("allowed_values"=>null, "sql"=>"attribute", "default_value"=>"", "is_null_allowed"=>false, "depends_on"=>array())));
@@ -609,7 +609,7 @@ class URP_ActionGrant extends UserRightsBaseClass
 		// Common to all grant classes (could be factorized by class inheritence, but this has to be benchmarked)
 		MetaModel::Init_AddAttribute(new AttributeExternalKey("profileid", array("targetclass"=>"URP_Profiles", "jointype"=> "", "allowed_values"=>null, "sql"=>"profileid", "is_null_allowed"=>false, "on_target_delete"=>DEL_MANUAL, "depends_on"=>array())));
 		MetaModel::Init_AddAttribute(new AttributeExternalField("profile", array("allowed_values"=>null, "extkey_attcode"=> 'profileid', "target_attcode"=>"name")));
-		MetaModel::Init_AddAttribute(new AttributeClass("class", array("class_category"=>"", "more_values"=>"", "sql"=>"class", "default_value"=>"", "is_null_allowed"=>false, "depends_on"=>array())));
+		MetaModel::Init_AddAttribute(new AttributeClass("class", array("class_category"=>"", "more_values"=>"", "sql"=>"class", "default_value"=>null, "is_null_allowed"=>false, "depends_on"=>array())));
 		MetaModel::Init_AddAttribute(new AttributeEnum("permission", array("allowed_values"=>new ValueSetEnum('yes,no'), "sql"=>"permission", "default_value"=>"yes", "is_null_allowed"=>false, "depends_on"=>array())));
 
 		MetaModel::Init_AddAttribute(new AttributeString("action", array("allowed_values"=>null, "sql"=>"action", "default_value"=>"", "is_null_allowed"=>false, "depends_on"=>array())));
@@ -646,7 +646,7 @@ class URP_StimulusGrant extends UserRightsBaseClass
 		// Common to all grant classes (could be factorized by class inheritence, but this has to be benchmarked)
 		MetaModel::Init_AddAttribute(new AttributeExternalKey("profileid", array("targetclass"=>"URP_Profiles", "jointype"=> "", "allowed_values"=>null, "sql"=>"profileid", "is_null_allowed"=>false, "on_target_delete"=>DEL_MANUAL, "depends_on"=>array())));
 		MetaModel::Init_AddAttribute(new AttributeExternalField("profile", array("allowed_values"=>null, "extkey_attcode"=> 'profileid', "target_attcode"=>"name")));
-		MetaModel::Init_AddAttribute(new AttributeClass("class", array("class_category"=>"", "more_values"=>"", "sql"=>"class", "default_value"=>"", "is_null_allowed"=>false, "depends_on"=>array())));
+		MetaModel::Init_AddAttribute(new AttributeClass("class", array("class_category"=>"", "more_values"=>"", "sql"=>"class", "default_value"=>null, "is_null_allowed"=>false, "depends_on"=>array())));
 		MetaModel::Init_AddAttribute(new AttributeEnum("permission", array("allowed_values"=>new ValueSetEnum('yes,no'), "sql"=>"permission", "default_value"=>"yes", "is_null_allowed"=>false, "depends_on"=>array())));
 
 		MetaModel::Init_AddAttribute(new AttributeString("stimulus", array("allowed_values"=>null, "sql"=>"action", "default_value"=>"", "is_null_allowed"=>false, "depends_on"=>array())));
diff --git a/core/attributedef.class.inc.php b/core/attributedef.class.inc.php
index 85789209f..ed15f836f 100644
--- a/core/attributedef.class.inc.php
+++ b/core/attributedef.class.inc.php
@@ -676,6 +676,21 @@ class AttributeClass extends AttributeString
 		parent::__construct($sCode, $aParams);
 	}
 
+	public function GetDefaultValue()
+	{
+		$sDefault = parent::GetDefaultValue();
+		if (!$this->IsNullAllowed() && is_null($sDefault))
+		{
+			// For this kind of attribute specifying null as default value
+			// is authorized even if null is not allowed
+			
+			// Pick the first one...
+			$aClasses = $this->GetAllowedValues();
+			$sDefault = key($aClasses);
+		}
+		return $sDefault;
+	}
+
 	public function GetAsHTML($sValue)
 	{
 		return MetaModel::GetName($sValue);
diff --git a/modules/itop-request-mgmt-1.0.0/model.itop-request-mgmt.php b/modules/itop-request-mgmt-1.0.0/model.itop-request-mgmt.php
index c8f3e4e55..3f4aaa693 100644
--- a/modules/itop-request-mgmt-1.0.0/model.itop-request-mgmt.php
+++ b/modules/itop-request-mgmt-1.0.0/model.itop-request-mgmt.php
@@ -50,15 +50,7 @@ class UserRequest extends ResponseTicket
 		MetaModel::Init_SetZListItems('standard_search', array('ref', 'title', 'org_id', 'start_date', 'status', 'caller_id', 'service_id', 'servicesubcategory_id', 'product', 'impact', 'urgency', 'priority', 'workgroup_id', 'agent_id', 'agent_email', 'related_problem_id', 'related_change_id', 'close_date', 'last_update', 'assignment_date', 'escalation_deadline', 'closure_deadline', 'resolution_code', 'solution', 'user_satisfaction', 'user_commment'));
 		MetaModel::Init_SetZListItems('list', array('ref', 'title', 'org_id', 'start_date', 'status', 'service_id', 'priority', 'workgroup_id', 'agent_id'));
 
-		MetaModel::Init_DefineState(
-			"frozen",
-			array(
-				"attribute_inherit" => 'assigned',
-				"attribute_list" => array(
-					'freeze_reason' => OPT_ATT_MANDATORY,
-				),
-			)
-		);
+		MetaModel::Init_OverloadStateAttribute('frozen', 'freeze_reason', OPT_ATT_MANDATORY);
 
 		// The freeze reason remains hidden in all other states
 		MetaModel::Init_OverloadStateAttribute('new', 'freeze_reason', OPT_ATT_HIDDEN);
diff --git a/modules/itop-tickets-1.0.0/model.itop-tickets.php b/modules/itop-tickets-1.0.0/model.itop-tickets.php
index 0aab5740d..e2b4fcccb 100644
--- a/modules/itop-tickets-1.0.0/model.itop-tickets.php
+++ b/modules/itop-tickets-1.0.0/model.itop-tickets.php
@@ -282,6 +282,14 @@ abstract class ResponseTicket extends Ticket
 				),
 			)
 		);
+		MetaModel::Init_DefineState(
+			"frozen",
+			array(
+				"attribute_inherit" => 'assigned',
+				"attribute_list" => array(
+				),
+			)
+		);
 		MetaModel::Init_DefineState(
 			"resolved",
 			array(